The invention relates to a knock-out mechanism for a press machine, and more particularly to such a device which includes apparatus for changing the timing of operation of the knock-out mechanism.
FIG. 6 illustrates a conventional knock-out mechanism on which a rotary shaft 1, in order to rotate synchronously with a press crankshaft, is integrally connected to a cam 3 by a key 2, and a lever 5 rotatably mounted by a supporting axle 4 has a roller 6 at one end thereof which contacts the cam 3. A pin 7 at the other end of the lever 5 is connected to one end of a knock-out rod 8.
The knock-out rod 8, in order to actuate a knock-out pin 9, is connected at its other end via a pin 10 to a lever 12 which is in turn mounted on a rotatable supporting axle 11.
A pin 14 links the knock-out pin 9 to a lever 13 which is mounted to the supporting axle 11 in the same manner as the lever 12. A cylinder unit for ensuring engagement between the cam 3 and the roller 6 includes a cylinder 15 which is mounted at one end to the press frame. The cylinder unit also includes a piston rod 16 which projects from the cylinder 15 to be linked with the lever 12 by a pin 17.
In the above prior art knock-out mechanism, the knock-out pin 9 travels within a die (a lower die in this case) to knock out a formed article, with the motion of the stroke being defined by the shape of the cam 3 rotated with the rotary shaft 1. Accordingly, the operator must choose a press machine suitable for the workpiece to be formed and also a knock-out unit which is adapted thereto so as to provide a stroke with an appropriate motion.
Further, circumstances may arise in which the knock-out timing must be changed in consideration of the manner of forming, in consideration of the workpiece to be shaped and in consideration of the transfer of workpiece. According to the prior art such as is illustrated in FIG. 6, however, in which the rotary shaft 1 is integrally connected to the cam 3 by the key 2, changing the knock-out timing by altering the rotational phase relationship between the cam and the rotary shaft is difficult. Inevitably, improper knock-out timing will result in products of inferior quality. On the other hand, while changing the knock-out timing by preparing various cams and choosing one suitable for the particular work to be performed may be possible, such an approach is inefficient and economically disadvantageous because it required much time and labor in order to exchange cams.